Filament-tensioning means



April 29, 1930. w RELYEA 1,756,882

' FILAMENT TENSIONING MEANS Filed Sept. 12, 1928 Inventor Walter I. Relgea H is Attorney.

Patented Apr. 29, 1930 STATE WALTER I. RELYEA, OF SGHENECTADY, NEW YORK, ASSIGN'OB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEVJ YORK FILAMENT-TENSIONING MEANS Application filed. September 12, 1928. Serial No. 385,499.

The present invention relates to electric discharge apparatus and pertains more especially to an improved support for the filamentary cathodes thereof.

In high power space current devices, the cathode usually comprises a filamentary member of substantial cross section and length and under operating conditions there may be considerable elongation of the heated member which may cause sag and. relative displacement with respect to the other electrodes. In the prior art devices, it has been customary to support the upper portion of the filament by means of a spring, which serves to tension the member in a longitudinal direction, hence maintaining the latter taut. However, it has been found that inasmuch as the position of this spring is directly above and close to the filament, in the hottest egion of the tube, the excessive heat may deleteriously affect the spring, rendering the material thereof brittle and cause it to lose a substantial portion of its resilience. In accordance with my invention, I have devised a structural arrangement which enables the removal of the tensioning spring some distance away from the highly heated zone, also which imparts a substantial 1glegree of heat insulation to the spring mem- An object of the present invention is to provide an improved tensioning support for the filamentary cathodeof high power vacuum tubes whereby the space relation between the cathode and other electrodes is maintained uniform despite the linear expansion of the filament during operation. A more general object is to improve the construction of electric discharge devices whereby the latter are accorded greater operating life. Further objects and advantages will be apparent as the specification is perused in connection with the accompanying drawing in which similar reference characteristics designate corresponding elements throughoutthe several views.

Fig. 1 shows an elevational view of a rectifier embodying the improved filament support; Fig. 2 is an enlarged view, partly broken away, of the upper portion of the filament supporting structure; Fig. 3 is a crosssectional view of the entire filament support,

while Fig. 4; is a view in perspective, partly broken away and in section, of a practical attaching means for the anode of the rectifier, including a convenient method of making a connection with the leading-in wire.

Referring to Fig. 1 numeral 1 designates an evacuated envelop which terminates in two oppositely directed reentrant stems 2 and 3. Numerals 4t, 4 indicate two filament lead wires which project through the stem 2 from suitable contact plugs, an inverted V shaped filament 5 being secured to the upper ends of said leads by fine binding wires 6. Due to the fact that in large power tubes, the lead wires may attain considerable length it is considered preferable to provide an insulating spacer which conveniently may take the form of a quartz block 7 into which are affixed two stifi wires arranged in staggered relation and secured to the filament conductors. About'the stem 2, there is fitted a cylindrical cap member 8 having a series of longitudinally and transversely extending slots, said cap member terminating in a circular plate 9 provided with a pair of apertures 10, 10 of relatively large diameter to allow-the filament conductors to pass therethrough with sufiicient clearance. In order to assure a tight fit between the cap member and the encompassed stem, a thin sheet 11 of copper mesh may be interposed between these elements. The plate member 9 serves as a base for two longitudinally extending metallic uprights 12, 12 which terminate some dis tance beyond the filament as shown more clearly in Fig. 2. The ends of the uprights are counterbored to receive small helical springs 13, 1.3, preferably of tungsten, the lengths of which are somewhat less than the depth of the bore. Springs of this type are usually heat treated in an atmosphere of hydrogen at a temperature of 1500 C. approximately so as to impart to them a permanent degree of elasticity. A U-shaped member 14 spans the two uprights and its ends project into the openings of the latter to rest upon the springs. There is a twisted strand member 15, preferably of molybdenum, wound tightly about member 14, approximately mid-way of the ends, and terminating in a loop through which the upper end of the filament is threaded. A small helix 16 of tungsten may be wound about the filament and positioned between the latter and member 15, so as to space these elements thereby precluding any weldingeffect at the place of contact between the loop and the heated filament. Obviously, the helix may, if desired, be affixed to the loop member instead of the filament. During the assembly of the filament structure, after the cap 8 has been forced over the stem 2, with the springs 13, 13 and member 1% in place, also with the lower ends of the filament securely bound to their respective conductors 4,4, pre sure may be exerted on the uprights 12, in direction longitudinally of the tube and away from the stem. This pressure serves to removethe slack in the filament 5, and to place the springs under compression. The clamps 1'7, 1'? may then be tightened so that the longitudinal position of the cap 8 on the stem be securely fixed. It is apparent that underoperating conditions, as the filament elongates, the

1 springs tend to take up the movement of expansion by pressing the member 14 away from the stem, hence, the heated member is maintained taut. Moreover the spring members serve to endow the filament with con siderable resilience which enables the latter successfully to withstand mechanical jar. It is also to be noted that the springs are removed from the hottest portion of the filament and further, that they are protected in substantial degree from the direct radiation of the latter by reason of the surrounding body of metal forming the upright members.

\Vhile it is evident that the subject-matter,

herein disclosed has application to all forms of electric discharge apparatus including oscillators, amplifiers and the like, also to incandescent lamps but particularly to those devices which employ large filament. structure susceptible to considerable elongation under operating conditions, I have exemplified the invention by illustrating a two-electrode rectifier. A cylindrical anode 18 of suitable metal may be concentrically mounted about the filamentary cathode by means of a slotted cap 19 which fits over the stem 3 similarly to the corresponding member attached to the cathode. The lower end of the cap may be closed by a metallic plate 20 having a central aperture 21. The plate member carries two longitudinally extending rods 22 which are aiiixed to the anode in any wellknown manner, for example, by welding. The lead 23 for the anode extend from an external plug through the stem and the aperture in the plate to make contact with the cap member 19in any suitable manner. However, I have found that this contact most conveniently may be produced by bringing the lead across the lower surface of the plate and secured by spot-welding in a groove porting the filament under tension, said means comprising a pair of uprights arranged remotely on opposite sides of the filament, a member spanning said uprights, a mechanical conn ction between said member and the filament and springs held under compression positioned between each end of said member and the adjacent upright whereby the springtensioning devices are removed from the region of the filament.

2. In an electric discharge device, an evacuated envelope containing a filament which normally tends to become slack under operating conditions, means for maintaining the filament taut, said means comprising a plurality of uprights supported from the envelope, a transversely extending member carried by said uprights, connecting means between said transverse member and said filament and a device held under compression positioned between said member and each upright.

3. In an electric discharge device, an evacuated envelope containing a filament which normally tends to become slack under operating conditions, and means for maintaining the filament taut, said means comprising a plurality of recessed uprights supported from the envelope, a spring positioned in each recess, a member spanning the uprights and having its ends located in the recesses in manner such as to place the springs under compression and a mechanical connection between said member and the filament.

4. In an evacuated envelope, a filament, a support therefor comprising a metallic loop member through which the filamentis threaded and to which the filament may normally adhere under operating conditions, means for preventing adherence, said means comprising a spacer between the loop member and the filament.

5. In an evacuated envelope, a filament, a support therefor comprising a metallic memher which normally contacts with the filament WALTER I. RELYEA. I I 

